INGM 423
EXAM SUMMARY 2014
Chapter 10 – Fundamentals of Metal Casting
Metals and Alloys
Solidification time of pure metals depend on the type of material, the thermal properties of the
casting material and the cast, the geometric relationship between volume and area as well as the
shape of the casting.
Cooling of pure metals with a definite solidus and liquidus with latent energy of fusion during the
freezing process. Casting freeze from the outside and travel inwards. Rapid cooling on the surface of
the casting creates solidified skin of fine equaxed grains.
Grains grow via homogeneous nucleation and the direction of growth is opposite to the direction of
heat propagation. As the heat driving force reduces the grains become more equated and coarse.
With alloys the freezing range is the temperature range between TL and TS which is and very
important factor of alloy solidification.
Effects of Cooling Rates
Slow cooling rates result in coarse dendrites with faster cooling rates result in finer dendritic
structures. Very fast cooling structures result in amorphous structures. Grain size has a dramatic
effect on material properties smaller grain size increases malleability and strength. Cracks and
segregation also decrease with smaller grain size.
Structure Property Relationships
Slow cooling rates in alloys results in uniform dendritic structures. Under normal cooling rates cored
dendrites are formed which different core structures have compared to the surfaces. Surfaces have
higher alloy concentration than the centres.
Micro segregation is involved with the difference in alloy composition in the surface and cores.
Dendritic structures have exactly opposite structures found in solid solution alloys. Has inverse
segregation and have higher concentration at the cores.
Fluid Flow
Molten metal flows through the sprue via the runners to the gates. Risers supply excess molten
metal during shrinking process. Slag, dross forms in a casting when Re exceeds 20000 can be
eliminated by vacuums, skimming or filters.
Fluidity of Molten Metals
Viscosity index increases fluidity increases. High surface tension decreases fluidity. Inclusions have a
detrimental effect on fluidity. Solidification pattern of the alloy influences fluidity and fluidity is
inversely proportional to the freezing range.
Casting Parameters – mold design, casting material and surface characteristics, degree of
overheating, rate of pouring and heat transfer.
Shrinkage
Shrinkage causes which causes dimensional changes which can sometimes lead to warping and
cracking. Shrinkage is causes by the contraction of the cooling liquid the contraction during
solidification and the contraction of the cooling solid metal.
Defects
Metallic Projections, Cavities, Discontinuities such as cracks cold or hot tearing and cold shuts.
Defective surfaces. Incomplete castings. Hot tears occur because casting cannot shrink freely during
cooling.
Porosity
Caused by shrinking and dissolved gases. Porosity can be avoided by making sure that there is always
enough molten material available while setting is taking place. Porosity can also be decreased by
increasing the temperature gradient by using chills. Gases can be removed from castings by flushing
with inert gases and casting into a vacuum.
Chapter 11 - Metal Casting Processes and Equipment
Expendable Mold, Permanent Pattern Casting Processes
Sand Casting
Tapers and angles in the mold air removal from the cast.
Shell Moulding
This is a type of sand casting. Metal form used to create sand cope and drag quite expensive for low
amounts of production. Mold is baked in an oven which determines the shell thickness. Smooth shell
inside providing low resistance. Suited for casting parts with sharp edges and thinner sections.
Lost Foam Process
Evaporative pattern casting. Metal cools faster than it usually would. Advantages include a simple
process, cheap flasks, polystyrene is cheap and has good formality, no finishing or cleaning needed.
Used in braking pads, cylinder heads and crankshafts.
Plaster Mold Casting
Gases formed during the process cannot escape and usually has to be casted in a vacuum. Presents
with good detail and surface finish also castings cool slowly which results in uniform grains. Limited
to nonferrous metals
Applications include, locks and lock components, gears, valves, fittings, tools and ornaments.
Ceramic Form Casting
Similar to plaster mold casting but with larger temperature variations. Good dimensional accuracy
and surface finish. Quite expensive. Applications include: Impellers, cutters for machines, mold for
metalwork, forms for plastics and rubbers.
Investment Castings
Applications include fine gears, cams and rotors of gas turbines.
Permanent Mold Casting
Used for pistons for cars, cylinder heads, connecting rods, gear blanks, appliances and kitchen ware.
Chapter 12 – Metal Casting: Design, Materials and Economics
Design considerations for casting: Shape of the part, casting process, parting line location, location of
the gates for feeding, runner geometry, proper controls and good practices.
Stress raisers that include corners angles, section thickness. Flat areas which can warp during cooling.
Shrinkage and cracking during cooling. Draft angles for better removal. Wide dimensional tolerances.
Uses of Metals:
Grey Cast Iron – Engine blocks, electric motor housings and pipes
Ductile Iron - Machine Parts, housings, gears, crankshafts
White cast iron – rolls for rolling mills, railroad car brake shoes, liners in machinery
Malleable Irons – railroad equipment, components for electrical applications
Chapter 13 – Metal Rolling Process and Equipment
To reduce rolling forces we can make use of smaller diameter rolls to reduce the contact area, taking
smaller reductions per pass, hot rolling to increase the fluidity of the metal or by applying front or
back tension to the strip.
Defects in rolled plates and sheets are wavy edges, zipper cracks, edge cracks and alligatoring.
Materials used in rolling are cast iron, cast steel, forged steel and tungsten carbide with small
diameter rolls.
Lubricants used in rolling processes are graphite, water based solutions, low-viscosity lubricants. For
hot rolling one uses compounded oils such as emulsions and fatty acids, cold rolling processed use
mineral oils or paraffin’s.
Different rolling processes:
Shape Rolling – channels, I-Beams and railroad rails
Roll forging or cross rolling – tapered shafts, leaf springs, table knifes or hand tools.
Skew Rolling - Ball Bearings
Ring Rolling – large rings for rockets and turbines, jet engine cases, gearwheel rims, ball bearing and
roller bearing races, flanges and reinforcing rings for pipes
Thread rolling - screws, bolts. Straight or tapered threads can be made on rods or wire. About 80
pieces per second can be produced, no material loss and cold working takes place to harden
material.
Rotary tube piercing – making of long thick walled and seamless pipe and tubing.
Diameters and thickness of pipes can be reduced by tube rolling.
Chapter 14 - Metal Forging Processes and Equipment
Forging is a process in which the work piece is shaped by compressive forces using various dies and
tooling.
Open Die Forging – solid work piece placed between two flat dies and reduced in height by
compressing it. Nails, pins, bolts, shafts
Closed die forging or impression die forging – work piece takes the shape of the cavity while being
forces between two shapes dies. Excess material flows outward and forms a flash.
Precision forging reduces the number of additional finishing operations required after forging and is
used to make gears, connecting rods and turbine blades.
Different forging operations:
Coining from a blank in closed die forging.
Heading is an upsetting operation used to increase the cross sectional area of a round rod or wire to
make nails, bolts heads and rivets.
Piercing – indenting of the surface of a work piece with a punch in order to produce a cavity or an
impression.
Hobbing – where a hardened punch with a particular tip geometry is pressed into the surface of a
block of metal. Cavity is used as die for forming operations.
Isothermal forging heats the die to the same temperature as the work piece.
Rotary Swaging – solid rod or tube is subjected to radial impact forces by a set of reciprocating dies
in a machine. Used to make screwdriver blades and soldering iron tips.
Tube Swaging - reducing the internal diameter of a tube with or without the use of a mandrel.
A material used to make a die must have strength and toughness at elevated temperatures,
hardenability and the ability to harden uniformly, Resistance to mechanical and thermal shocks, wear
resistance
Common die materials are chromium, nickel, molybdenum and vanadium. Dies are made by various
methods that include casting, forging, machining, and grinding also electrical and electrochemical
methods.
Die failures can be attributed to - improper design or material selection or manufacturing which
implies the heat treatment and finishing process. Excessive wear, overloading, improper alignment
or handling.
Chapter 15 - Extrusion and Drawing of Metals
In general a billet is forced through a die. Most of these products have a constant cross sectional
area, the process can be performed at room temperature. Each billet has to be extruded separately
and thus the process is semi continuous.
Examples of extruded products are guides for sliding doors, tubing, and structural forms for
architectural purposes, door and window frames, brackets, gears and hangers.
Materials used for extrusion are aluminium, copper, steel, magnesium and lead.
The Extrusion Process
Usually a round billet is placed in a cylindrical container and forces by a hydraulic ram through a die.
Variables in extrusion are the extrusion angle or die angle, the reduction in cross section, extrusion
speed, billet temperature and lubrication all of this have an effect on extrusion pressure.
Extrusion in Practice
Metals with high malleability are easily extruded. R value is usually between 10 and a 100. R values of
at least 4 should be used for less malleable materials. Final products usually shorter than 7m.
Products with smaller diameter have to be made with stretching.
Warm Extrusion
Uses high temperatures to extrude materials that are not malleable at room temperatures, this
reduces the forces needed for extrusion.
Special considerations for warm extrusions are: die wear can be excessive, cooling of the warm billet
can cause problems, dies have to be preheated, oxide layers form which help with abrasion.
Glass is an excellent lubricant for extruding steel and other alloys. Glass melted at high temperatures
which lubricates the surfaces. When designing dies try for a symmetrical die with no sharp corners.
Cold Extrusion
Advantages over hot extrusion are:
Improved mechanical characteristics because of work hardening.
Better tolerance control which decreased the need for machining to finish the product.
Better surface finish, also eliminated the need to harden the billets. Has a very competitive
production cost.
Factors to consider in cold extrusion are: large tensions on the equipment while extruding. Hardness
ranger from 58 – 65 HRC. Lubrication is extremely important and is usually a phosphate layer
followed by soap or wax.
Impact Extrusion
Toothpaste holders.
Hydrostatic Extrusion
At a pressure of 1400 Mpa usually, vegetable oil used at low temperatures as lubricant at higher
temperatures glass, wax and polymers are used.
Extrusion Defects
Surface Cracks
Usually occurs because of too high temperature or too high speed of extrusion. These cracks are
usually inter-granular. Also occurs when the product is stuck in the die. Bamboo effect is when the
pressure cycles between high and low as static friction is overcome.
Internal cracks occur because of hydrostatic tension.
Chapter 16 – Sheet Metal Forming
Metals used for sheet metal purposes are usually – Lightweight, cheap, quite strong, carbon steel.
Shearing with a Punch and Die
Plate is cut with shear tension. Sides are not cut perpendicular or smooth, and cracks exist above and
below the shear positions and they grow in the process until they meet. Clearance is the main factor
in shearing with a punch and die and determines die shape and roughness of the sides. Velocity of
the punch is also very important.
Fine Blanking
Smooth square edges, v-formed stinger holds the plate in position and prevents distortion. Tripped
press usually used, punch movement, movement of the pressure surface.
Slitting with rotary knifes
Shearing Dies
Clearance is usually a function of the type of material, its thickness and other characteristics. Softer
materials can have a smaller clearance than harder materials. Thicker plates need a larger clearance.
Smaller holes need a larger clearance.
Compound dies are expensive and the process is quite slow more than one operation performed at
one station.
Progressive dies as with the top of an aerosol can.
Transfer dies uses different operations at different stations.
Die materials usually consist of carbide steels.
Spring back
Methods of eliminating spring back are to over bend the plate or bend it over a form which is known
as coining.
Common bending operations
Press brake forming for small operations, easily automated simple equipment and adaptable.
Roll bending – plates are bent using a series of rollers. Distance of rollers determine the bend
curvature.
Bending in a four sided machine – bending synchronized with vertical movement.
Bead Forming – can be done with a single die or with two dies and a press brake. Removed sharp
metal edges
Dimpling first presses a hole through the sheet and then bends is to about 90 degrees, with flaring
the angle is smaller than 90 degrees.
Hemming is a 180 degree bend where edges are completely bend flat increases material stiffness and
removes shaft edges.
Roll forming – metal bend in stages by a sequence of rollers for continuous lengths and long pieces of
sheet metal. Channels, gutters, rain water piping and panels. Rollers made from grey iron or cast iron
and coated with chrome. Lubrication increases life and surface finish.
Methods for Bending Tubes
To prevent the collapse of tubes while bending one needs special techniques, filling with sand and
inserting mandrels while bending is one such method.
Bulging is when n pipe is places in a two part female die and then bent with a liquid to the shape of
the female die. Water and coffee flasks are manufactured with this method, outlet manifold also
made with this method.
Bellows
Radial shaped dies placed within a pipe and repeatedly shapes. Cheap for mass production
Stretch forming process
Used for products with cylindrical and box shapes such as pots, pans, fuel tanks and cool drink cans.
Chapter 17 – Powder Metal Processing and Equipment
Metals are compacted into desired and often complex shapes and sintered without melting them to
form a solid piece.
Powder Metallurgy process –
Powder production
Blending
Compaction
Sintering
Finishing Operations
Process Capabilities – High production rates on complex parts, good dimensional control, and
elimination of finishing and machining operations.
Powder Metal production by atomization – gas atomization, water atomization, atomization with
rotating consumable electrode, centrifugal atomization with spinning.
Mechanical Commination to Obtain Fine Particles – roll crushing mill, ball mill, hammer milling
Design considerations for PM parts –
The shape of the compact must be as simple as possible, provision must be made for the ejection of
the green compact without damaging it, walls should not have a too high aspect ratio, steps in parts
can be produced if they are simple and their size does not exceed 15% of the overall length, letters
can be pressed if perpendicular to the pressing direction, flanges and overhangs can be produced by
a step in the die, true radius cannot be pressed instead use a chamfer, tolerances 0.05 to 1 mm
Chapter 18 - Ceramics, Glasses and Superconductors
Shaping processes for ceramics - casting, slip casting – large and complex parts, plumbing ware, art
objects and dinnerware.
Plastic forming – Extrusion, injection molding, molding and jiggering
Pressing – wet pressing, isostatic pressing, injection molding and hot pressing
Drying and firing/sintering – Reduce moisture.
Forming and shaping of glass is done by:
Flat sheet and flat plate glass – float method, drawing and rolling
Tubing and Rods – Product is drawn and a hollow mandrel is used where air is blown through.
Extrusion process.
Strengthening and annealing glass – thermal tempering where the surface of the hot glass is cooled
rapidly by a blast of hot air
Chemical tempering – heated in a bath of potassium or sodium oxides
Laminated glass and bulletproof glass with polymer or plastic between two layers of glass.
Chapter 19 – Plastics and Composite Materials: Forming and Shaping
Variations in the extrusion process and the parts produced – plastic piping and tubes, spider die.
Rigid plastic tubing, rotating die, polymer sheets and films, flat extrusion die
Melt spinning process for producing polymer fibres.
Types of moulds used in the injection moulding process is the two-plate mold the three-plate mold
and the hot-runner mold.
Reaction injection moulding process typically used to make water skis and car body panel parts or
thermal insulation.
Rotational moulding process – thin walled metal mold with two parts made to be rotated about two
axis and is used for making trash cans, buckets and plastic foot balls.
In thermoforming the sheet of plastic is heated to the sag point of the polymer and is forced against
the mold surface by using air pressure or a vacuum. Products are refrigerator lining, advertising signs
packaging and trays.
In compression moulding a pre-shaped charge of material is placed directly into a heater mold cavity
and formed under pressure from a plug or from the upper half of a die. Products are dishes, handles,
container caps and housing.
Chapter 20 – Rapid Prototyping Operations
Advantages of rapid prototyping would be – the model can be manufactured in hours, this can be
used in the subsequent manufacturing processes. The three major groups in prototyping would be
subtractive, additive and simulation or virtual.
The subtractive process serves as shape verification and polymer or wax is used to manufacture the
working piece.
Additive processes – Fused deposition modelling
Stereo lithography - curing of a liquid polymer into a specific shape by using a laser which generates a
ultra-violet beam. This laser is focussed on a certain parts of the liquid at a time.
Multijet/polyjet modelling – like an ink jet printer where print heads deposit a photopolymer on a
build tray.
Selective laser sintering – sintering of metallic or non-metallic powders selectively into an individual
object. A laser sinters a particular cross section into a solid mass.
Electron beam melting – uses electron beam to melt chrome or titanium powder into a specific
shape. For metal prototype.
Three dimensional printing where a printing head deposits an inorganic binder material onto a layer
of polymer, ceramic or metallic powder.
Laminated object manufacturing used to make crank shaft.
Rapid prototyping can be used to make blanks for investment casting
Chapter 21 – Fundamentals of Machining
Removal of metal by forming metal chips during cutting. Important processes are straight turning,
cutting off, slab milling and end milling.
Relief angle between the tool and material on the rear, shear angle between bottom tip of tool and
top of material, rake angle degree of tool slanting. Called orthogonal cutting and has a well-defined
shear plane.
Types of chips produced in the orthogonal cutting processes are – continuous chips, built up edge
chips, serrated or segmented chips and discontinuous chips.
Continuous chips are formed when malleable metals are cut using high speeds or rake angles shear
takes place in a very fine shear zone. Gives good surface finish. Chips can be caught up in tools. Chip
breakers can solve these problems.
BUE Chips – because of work hardening and layer forming the chips can become hard. As the cutting
speed increases so does the size of the BUE. The following factors decreases the likelihood of built up
edges.
Decreasing the cutting depth, increasing the rake angle, sharp cutting equipment, and effective
cutting fluid.
Serrated or segmented chips - semi continuous chips with area of high and low stresses. Metals with
low thermal conductivity and strength that decreases rapidly with temperature cause this kind of
chips. TITANIUM
Discontinuous chips usually arise under the following circumstances – brittle material, work pieces
that contain hardening inclusions and impurities, very high and very low cutting speed, low rake
angles, ineffective cutting fluids and low machine stiffness or rigidity.
Soft materials do not work well with chip breakers. Machine them with stopping or short reverse
movement periods. Plastics react the same manner.
Temperature effects during cutting is as follows – when the temperature reses too much it adversely
effects the hardness, resistance to wear of the cutting equipment. When temperature is propagated
unevenly the machine can warp and distort.
Two types of wear can occur in cutting equipment – crater wear and flank wear, flank wear occurs on
the relief side of the cutting equipment due to high temperature and abrasion. Crater wear occurs
on the rake face.
Factors that influence the surface finish of a product is. BUE this has the largest effect on surface
finish and causes scuffing marks. Ceramic and diamond edges cutting tool are usually the best for
surface finish.
Dull cutting tools causes large radii along the cutting surface.
Chapter 22 – Cutting Tools and Cutting Fluids
Cutting equipment must have the following characteristics – hardness at high temperatures,
toughness to be able to absorb impacts, wear resistance for a good life, must be chemically stable.
Carbon and medium alloy steel – advantages are being cheap, shapes into forms easily and
sharpeners easily. Disadvantages are is not being able to keep functioning under higher
temperatures also weak wear characteristics.
High speed steel – for high speed applications, contains the most alloys, can be hardened to different
values available in wrought cast and sintered forms.
Cast cobalt alloys – should not be used at higher speeds, stellite tools, good resistance to wear and
keeps hardness at higher temperatures, however no toughness at higher temperatures and quite
brittle.
Carbides remain hard over a wide variety of temperatures. High thermal and electricity conductivity,
very cost effective.
Tungsten carbide cutting tools where tungsten particles are bonded with a cobalt matrix. As cobalt
increases the strength, hardness and resistance wear decreases however toughness increases.
Coatings must have the following characteristics – high strength, toughness can be abrasive or
chemically reactive.
Coating material are tininiumcarbide, tataniumnitride, and ceramics and are usually deposited using
chemical vapour deposition or physical vapour deposition.
This results in larger surface strength with lower friction and less build-up also results in a smoother
and more uniform cut.
Ceramics or aluminium based ceramics, white or cold pressed ceramics, high resistance wear and
hard at very high temperatures. Chemically stable thus no build up. Able to cut at very high speeds.
Very low toughness.
Cement used for chip breakers
Cubic Boron Nitride – hardest substance on earth after diamonds. Made by sintering a 1mm layer of
polycrystalline cubic boron nitride on a ceramic substrate. The carbide provides the shock resistance.
Cutting fluids not used, material very brittle all other characteristics are excellent.
Silicon nitride ceramics should not be used for iron and steel rather be used with cast iron and nickel.
Types of cutting fluids – oils, emulsions, semi-synthetic materials, synthetic materials.
Fluid cooling used in gun-drilling and end milling.
Mist cooling provides cooling liquid to unreachable areas. Better working piece visibility. Ventilations
required for cooling.
High pressure systems aids in cooling ability and can serve as a chip breaker.
Chapter 23 – Machining Processes Used to make Round Shapes
Lathe usually specified by the following characteristics - maximum workable diameter that can be
machined, the maximum length that can be handled, length of the bed.
The following operations can be performed on a lathe, cutting of thread, boring, drilling, grooving
Bring considerations – boring shaft must be strong enough to minimize deflections, vibration must be
avoided
Troubleshooting guide for turning –
Tool Breakage – Tool material lacks toughness, improper tool angles and machine lacking stiffness,
worn bearings or machine components.
Excessive tool wear – machining parameters too high, improper tool material, ineffective cutting
fluid.
Rough surface finish – built-up edge on tool, feed too high, tool too sharp, chipped tool, vibration
and chatter
Dimensional variability – lack of stiffness of machine and work holding devices, excessive
temperature rise and tool wear
Tool chatter – lack of stiffness in machine and tool and work holding devices, excessive tool
overhang, and machine parameters not set properly.
Chapter 24 - Machining Processes
Conventional milling – biggest chips at the end of the cut, very smooth process with sharp tool also
known as up milling.
Climb milling or down milling – cut starts at the surface where the chips are the biggest. Downwards
forces keep the working piece in position, shortens the tool lifetime and is typically used in CNC
programmable machining processes.
Face milling typically uses a wiper to obtain a smooth surface finish.
Ball nose end milling
Straddle milling, form milling, slotting and slitting (Through Cut)
Breakout can be decreased by increasing the lead angle.
Cutting vibration can be reduced by mounting the cutter as close as possible to the base and by using
the correct type of cutter. Chamfers always better than radius.
Broaching good dimensional accuracy and surface finish used to create slots in gears. For broaching
the design must keep in mind that the part has to be able to be clamped. Also used in gun barrels.
Various methods of producing gears, by form cutting from a blank, gear generating with pinion
shaped cutter, gear generator with rack shaped cutter also by hobbing.
Gears finished by grinding
Chapter 25 – Machining Centres, Machine Tool Structures and
Machining Economics
Chapter 26 - Abrasive Machining and Finishing Operations
Must be hard materials with grains that are able to break, self-sharpening ability.
Aluminium oxide in fused and unfused forms – fused is darker and less breakable or white and
breakable. Unfused is harder with smaller grain sizes. Holds sharpness better.
Super grinding materials are diamond and cubic boron nitride.
Binding types for grinding tools - vitrified usually glass or a type of ceramic, resiniod has an organic
composition.
Grinding is the removal of chips using individual abrasive parts as the cutting part. Grinding
compared to other cutting processes has a much higher cutting speed also chips undergo much more
deformation as in other cutting processes.
Temperature gradients change the surface characteristics and results in tension or stress in the work
piece.
Ultrasonic machining is done with abrasive slurry and ultrasonically vibrating tools, good for
machining brittle materials like glass.
Chapter 27 – Advanced Machining Processes
Chemical machining – small amounts of material removed from the surface, used for deburring,
engraving of metals, printed circuit boards and micro-processors. Blanking of thin metal plates also
possible. Low tool cost and suites for low production numbers.
Electro – chemical machining – reverse of electro plating. Electrolyte reacts if a current carrying
interacts with high rates of electrolyte flow and washes away the ions on the metal surface before it
can react with the cathode. Formed machinery made form copper or bronze or brass. The electrolyte
is a highly conductive electrolytic salt. Can create complex shapes with deep holes, such as knee
implants. Expensive high power usage and expensive equipment.
This process not suited to manufacture sharp edges or flat bottoms. Unequal holes are difficult to
create because electrolyte flow can be hard to accurate manage. Holes will be slightly tapered.
Electrochemical grinding process, same as usual grinding however grinding wheel is rotating cathode
with abrasive particles. Cutting or grinding of very hard materials, used in the honing process and is
about five times faster. Electrical honing used to finish cylinders on the inside.
Electrical discharge Machining (EDM) – erosion by spark discharge used to sink dies, holes in fuel
injection nozzles. Direct current usage using shapes electrodes and work piece in dielectric fluid.
Form cutting of complex shapes and very hard material.
Design considerations are – electrode has to be cheaply manufactured for the part no intricate
shapes, deep grooves and slots have to be avoided. Surface finish can’t be too important.
Wire EDM suited for cutting extremely thick billets.
Laser Beam Machining (LBM) – focussing of optic energy on working piece, evaporates porosities in
the metal. Cannot be used on very reflective metals.
Electron Beam Machining – high velocity electrons hit the surface of the material and causes heat,
fast process with good surface finish, cutting and punching of thin plates. Very small holes and slots.
Design considerations are the vacuum chamber has a limit size capacity.
Water jet cutting - can be started in any part of the component, no heat generated, minimal burr
generations.
Abrasive WJM – contains silicon carbide and aluminium oxide, suited for heat sensitive material, cuts
up to 25mm thick.
Chapter 30 – Fusion Welding Processes
Oxyfuel-gas welding - any process that uses a gas combined with oxygen to create a flame.
Gas tungsten arc welding – non usable electrode tungsten typically used with shielding gas. Known as
TIG welding TUNGSTEN INHERT GAS. Filler metal added by hand in wire form. Filler metal same as
the working piece. Can be used without filler material.
Plasma arc Welding – concentrated plasma arc formed, plasma is ionised warm gas made of equal
amounts electrons and ions. Transferred where the working piece is part of the circuit and nontransferred where the work piece is not part of the circuit. Less thermic distortion and high welding
rate.
Shielded metal arc welding – heat energy electrically obtained. Also known as arc welding usable
electrode. The electrode coating deoxidizes the surrounding area during welding and protects the
weld environment against oxidation and oxygen.
Submerged Arc Welding – weld is shielded by granular flux made from lime, silica and magnesium
oxide. Usable electrode winded in wire form.
Gas metal arc welding – welding area shielded by inert gas argon helium and carbon dioxide, also
known as MIG welding for metal inert gas. Also uses usable electrode fed through the welding gun on
request.
Fluxed – Cored Arc – Welding – similar to MIG welding however the electrode is a tube that contains
and feeds flux towards the welding, the process is more stable than arc welding, also better
mechanical properties.
Electro-gas – Welding – welding vertical edge sections. Spaces cooled by two water controlled copper
dams. Electro-slag welding vertical sections between two plates.
Thermite welding with sand mold and gap between welding elements.
Electron bundle welding – similar to electron beam machining instead used for welding.
Laser beam welding – used to weld razors blades, deep penetration and very dense material welding
possible due to much focussed beam. Can be pulsed for spot welding. Minimum warping and
distortion weld present with good ductility and free from brittle areas. Process easily automated.
Advantages of LBW above EBW no vacuum is needed for the process, laser can be formed
manipulated and focussed as needed. Laser beam does not cause x-rays, better quality weld.
Discontinuities and defects in welds – bridging incomplete fusion in fillet welds, incomplete fusion
from oxide or dross especially in aluminium, incomplete fusion in groove weld.
Under fills, exclusions, porosity, cracks and incomplete penetrations are examples of weld defects.
Overlaps and undercuts also occur at the edges of welds.
Stress relieving of welds can be done by pre-heating the base metal, control the cooling rate.
Inclusions are oxides or fluxes trapped inside the welding zone.
Functions of electrode coatings – stabilize the arc, generate gas that provides shielding against the
atmosphere, control the rate at which the electrode melts, acts as flux to protect the weld against
the formation of oxides.
High carbon steel have very weak weld ability. Effects of distortion important in all welds.
Non-ferrous metals weld able at high rates of heat input.
Non-destructive testing includes visual inspection, x-rays, magnetic particle testing , liquid
penetration and ultrasonic.
Need for edge penetration should be avoided or minimized. Weld bead size as small as possible.
Design considerations for welds – loads must be on welds as far as possible, components must be
square cut, burrs to be removed, welds far away from cylindrical sections can be influenced by
warping, and welds should be kept away from machining surfaces.
Chapter 31 – Solid State Welding Processes
Process in which joining takes place without fusion at the interface of the two parts that are to be
welded.
Phenomena in solid state welding – diffusion, pressure
Cold welding and roll bonding – pressure is applied to the work piece by dies and rolls, at least one of
the mating parts has to be able to undergo plastic deformation, bonding of aluminium and steel,
stainless steel and mild steel.
Ultrasonic Welding – the faying surfaces of two components are subjected to static normal stress and
oscillating shear stresses. Used in joining plastics, packaging with foils, lap welding of sheets.
Interrupted internal surfaces should be avoided.
Friction welding – heat required for welding generated by friction. One component remains
stationary while the other is moved. One of the components has to have rotational symmetry.
Friction Stir Welding – welding for aluminium alloy plates.
Resistance welding – heat required for welding is produced by electrical resistance across the two
components that have to be joined.
Resistance Spot welding - used in automobile body assembly for sheet metal fabrication. The tips of
two opposing solid cylindrical electrode touch a lap joint of two sheet metals and the resistance
heating produces a spot weld. Attach handles to stainless steel cook ware.
Test methods for spot welding are, tension shear test, cross tension test, twist test.
Resistance Seam Welding – the electrodes are replaced by rotating wheels or rollers. Used to make
longitudinal seams in cans, gasoline tanks and other containers.
High frequency resistance welding or butt welding – high frequency current is employed production
of butt welded tube or piping. Structural sections of tubes or I beams can also be manufactured.
Resistance Projection Welding – high electrical resistance at the joint is developed by embossing one
or more projections on one of the surfaces that has to be welded. For joining of a network of rods
and wires, metal baskets, grills, oven racks and shopping carts.
Flash welding – flash welding process for end to end welding of solid rods or tubular parts. Heat is
generated very rapidly form the arc as the ends of the two members begin to make contact and
develop electrical resistance at the points. Not it is preferred that the two welded parts have the
same diameter. Joining of pipe and tubular parts for metal furniture and windows.
Stud welding – used for welding bars, threaded rods and fasteners to metal plates. The stud serves as
one of the electrodes while being joined to the other components. Used in building construction.
Percussion welding – the electrical energy required for welding is stored in a capacitor. Process is
useful where heating of components adjacent to the joint is to be avoided. As in electronic
assemblies and electrical wires.
Explosion welding used to weld titanium and low carbon steel.
Diffusion welding used in aerospace industry, primary strength form diffusion of molecules, suitable
for joining dissimilar metals or substances.
Chapter 32 – Brazing, Soldering, Adhesive Bonding and Mechanical
Fastening Processes
Brazing is a liquid solid state process, the process in which the filler metal is placed between the
faying surfaces to be joined and the temperature is raised sufficiently to melt the filler metal.
Furnace blazing incorporates where a shaped wire melts and moves into clearances by capillary
action.
Methods of brazing alteration in the source of heat – torch, furnace, induction, resistance, dip,
infrared, diffusion, high energy and braze welding.
Good brazing design incorporates – enough bonding area to for shear forces and sufficient bonding
area.
Soldering – low surface tension and high wetting ability.
Copper, silver and gold solders well iron and nickel medium, steels and cast irons as well as harder
material difficult.
Soldering techniques, torch, furnace, iron, induction, resistance, dip, ultrasonic and reflow.
Properties for adhesive bonding – strength, toughness, resistance to fluids and chemicals, resistance
to environmental degradation, capability to wet surfaces that have to be bonded.
Good bonding design is one with the largest surface area.
Advantages of adhesive bonding – interfacial bond has sufficient strength, distributes the load on the
interface, external appearance unaffected, very thin and fragile components can be bonded, material
with very different properties can be bonded.
Limitations of bonding – limited range of service temperatures, bonding time can be long, limited
reliability.
Design considerations for bonding – only compressive, tensile and shear forces. No peeling cleavage.
Employ single taper, double tapered of bevelled designs to increase bonding area.
Mechanical fasteners – increases the frictional resistance between materials.
Design guidelines for riveting, one has to be able to punch both sides, exposed shank must not be too
long, should be placed sufficiently far from edges to avoid stress concentrations, section curvature
should not interfere with riveting process.
Other fastening methods – stitching and stapling, seaming, crimping, spring and snap in fasteners
Advantages of mechanical fasteners – ease of manufacture, ease of assembly and disassembly, easy
to create designs with moveable joints. Lower overall manufacturing cost.
Design considerations for fasteners – type of loading, distance and size of holes, spacing of holes,
compatibility of material and fasteners. Use minimum number of fasteners
Cost of operations –
Highest – brazing bolts and nuts
Intermediate – riveting and adhesive
Lowest – seaming and crimping